MathContexts in BigDecimals - ScalaCheck generator creates BigDecimals which can't be serialized then deserialized. How to use MathContexts correctly?

Question

I discovered an issue in Scalacheck whereby arbitrary[BigDecimal] would generate BigDecimals which could not be converted to Strings and then back into BigDecimals, and I'm trying to work with the creator to find a fix for it, but I'm unsure of how the MathContexts come into play.

The original generator looks like this:

/** Arbitrary BigDecimal */
implicit lazy val arbBigDecimal: Arbitrary[BigDecimal] = {
  import java.math.MathContext._
  val mcGen = oneOf(UNLIMITED, DECIMAL32, DECIMAL64, DECIMAL128)
  val bdGen = for {
    x <- arbBigInt.arbitrary
    mc <- mcGen
    limit <- const(if(mc == UNLIMITED) 0 else math.max(x.abs.toString.length - mc.getPrecision, 0))
    scale <- Gen.chooseNum(Int.MinValue + limit , Int.MaxValue)
  } yield {
    try {
      BigDecimal(x, scale, mc)
    } catch {
      case ae: java.lang.ArithmeticException => BigDecimal(x, scale, UNLIMITED) // Handle the case where scale/precision conflict
    }
  }
  Arbitrary(bdGen)
}

The problem lies within the fact that the BigDecimal constructor used inverts the sign of the scale argument, thereby making Int.MinValue turn into a scale bigger than 2^32 -1.

scala> val orig = BigDecimal(BigInt("-28334198897217871282176"), -2147483640, UNLIMITED)
orig: scala.math.BigDecimal = -2.8334198897217871282176E+2147483662

scala> BigDecimal(orig.toString)
java.lang.NumberFormatException
  at java.math.BigDecimal.<init>(BigDecimal.java:554)
  at java.math.BigDecimal.<init>(BigDecimal.java:383)
  at java.math.BigDecimal.<init>(BigDecimal.java:806)
  at scala.math.BigDecimal$.exact(BigDecimal.scala:125)
  at scala.math.BigDecimal$.apply(BigDecimal.scala:283)
  ... 33 elided

The core of the fix is to increase the lower bound by the number of digits in the unscaledVal, but I only thought of a way to do it with only MathContext.UNLIMITED. I fear we miss out on generator robustness if we do that:

lazy val genBigDecimal: Gen[BigDecimal] = for {
  unscaledVal <- arbitrary[BigInt]
  scale <- Gen.chooseNum(Int.MinValue + unscaledVal.abs.toString.length, Int.MaxValue)
} yield BigDecimal(unscaledVal, scale)

So, if we want to keep using the other MathContexts, what do we have to do to ensure we use them correctly?